The present invention generally relates to semiconductor processing, and in particular to a system and method for applying an edge bead removal material to the edge of a photoresist material layer disposed on a semiconductor wafer.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon structure is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist material, thickness uniformity of the photoresist material is a significant factor in achieving desired critical dimensions. The photoresist material should be applied such that a uniform thickness is maintained in order to ensure uniformity and quality of the photoresist material layer. The photoresist material layer thickness typically is in the range of 0.1 to 3.0 microns. Good resist thickness control is highly desired, and typically variances in thickness should be less than xc2x110-20 xc3x85 across the wafer. Very slight variations in the photoresist material thickness may greatly affect the end result after the photoresist material is exposed by radiation and the exposed portions removed.
Application of the resist onto the wafer is typically accomplished by using a spin coater. The spin coater is essentially a vacuum chuck rotated by a motor. The wafer is vacuum held onto the spin chuck. Typically, a nozzle supplies a predetermined amount of resist to a center area of the wafer. The wafer is then accelerated to and rotated at a certain speed, and centrifugal forces exerted on the resist cause the resist to disperse over the whole surface of the wafer. The resist thickness obtained from a spin coating process is dependent on the viscosity of the resist material, spin speed, the temperature of the resist and temperature of the wafer.
After the photoresist is spin coated onto the wafer, a rim or bead of photoresist remains on the edge of the wafer. This rim or bead is removed by applying an edge bead removal solvent by using an edge bead removal (EBR) nozzle, so that loose particles from the rim or bead do not become a source of contamination that can cause wafer defects. Typically, the solvent is either applied at the bottom edge of the wafer, while the wafer is spun causing the solvent to wick around the edge and wash off the photoresist bead or the solvent is applied on the top outside edge of the wafer. However, applying the solvent to the top edge of the wafer has its own inherent problems. One of the problems is that when the solvent spray or jet is shut off, a drop of solvent can remain in a nozzle tip of the nozzle, and may free fall onto the wafer undesirably dissolving useful portions of the photoresist material layer, thus destroying the uniformity of the wafer ultimately causing wafer defects.
Another problem is that when the solvent stream is dispensed onto the surface of wafer edge at a relative high angle ( greater than 30 degree relative to horizontal wafer plane), splashes are produced that became airbone particles. The airbone solvent particles inside the coater cup will eventually fall back onto wafer surface after resist coating causing pinholes in the resist film or localized resist film thickness variation. Consequently, following exposure with a mask and development, the resist pattern will be deformed then transferred to final etch pattern, resulting in yield loss.
FIG. 1 illustrates a typical conventional edge bead removal system 10. A wafer 34 is vacuum held onto a rotating chuck 32. The wafer 34 is spin rotated by a shaft 30 driven by a motor (not shown). A stand 12 supports a rotatable handle 14 for rotating a edge bead removal nozzle assembly 20 above the edge of the wafer 34. An L-bracket 16 is coupled to a support bracket 18, which holds a nozzle bracket 22. The nozzle bracket 22 holds the tip of an edge bead removal nozzle 26 at a fixed angle 24. Fixed angle 24 is typically above 45xc2x0 and results in splashing of edge bead removal solvent splashes.
Another system for removing an edge bead on a wafer that alleviates the problem of solvent use is known as an optical edge bead removal system or track system such as the family of CLEAN TRACK(copyright) systems manufactured by Tokyo Electron Limited, Inc. in Tokyo, Japan. Such track systems are used in the various modes of photoresist processing. However, for thick resist film applications (greater than 1.5 micron), optical EBR alone is not adequate due to low power output of exposure source on the track systems and throughput constraint. The current solvent nozzle designs employed on most track equipment are not effective in reducing solvent splashes on wafer surface during edge bead removal. Solvent splashes will dissolve resist material or cause partial thickness loss leading to distorted pattern upon exposure. This type of bad pattern transfer will eventually result in IC device failure and/or yield loss. If the edge bead removal process employs back-side solvent dispense and/or optical methods only, the resist edge bead removal process will be less than optimal and residual resist will be left around wafer edges. These residual resist particles can flake off during an etch or ion implantation process causing defects on the wafer.
In view of the above, an edge bead removal nozzle is needed that ensures that droplets formed at a nozzle tip of the nozzle do not fall onto a photoresist material layer that is being worked upon.
The present invention relates to an edge bead removal system and method that employs a nozzle for applying edge bead removal solvent to an edge bead of a photoresist material layer disposed on a wafer. The edge bead removal solvent can be a developer, a rinse or a cleanser. A fine stream of solvent is dispensed from a fine, needle-like nozzle. The nozzle of the present invention eliminates solvent splash by lowering the angle of dispense to less than 20xc2x0 as well as providing more degrees of freedom to the nozzle arm adjustments. The present invention employs adjustment screws and a built-in protractor to precisely set the application angle. The nozzle of the present invention includes a clamp design having a nozzle body clamp which holds the nozzle and a main shaft with a protractor assembly for up and down angle adjustments. A support bracket is coupled to the protractor assembly and allows for pivoting and side to side movement of the protractor assembly and the support bracket with respect to one another. A clamp connects a main arm structure that moves the entire edge bead removal nozzle assembly over the wafer. The nozzle assembly of the present invention is particularly useful for removing edge beads formed on photoresist material layers having a thickness equal to or greater than 1.5 microns thick.
One particular aspect of the invention relates to an edge bead removal system that includes an edge bead removal nozzle having a processor for controlling the application angle. The processor is coupled to a user interface that allows a user to set the application angle. Defect analysis can then be used to determine an optimal application angle for a given production run. The processor is also coupled to a stepper motor that rotates the nozzle to the desired application angle. A protractor component provides verification of the programmed application angle. An alternate edge bead removal system utilizes a measurement system adapted to measure defects on the wafer after edge bead removal. The measurement system is coupled to the processor and provides for automatic adjustment of the application angle.
Another aspect of the present invention relates to an edge bead removal system for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The system comprises an edge bead removal nozzle assembly having an adjustable application angle and an arm coupled to the edge bead removal assembly. The arm is adapted to move the nozzle assembly between a rest position and an application position.
Another aspect of the present invention relates to an edge bead removal nozzle assembly for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The nozzle assembly comprises an edge bead removal nozzle disposed in a nozzle bracket and a protractor component coupled to the nozzle bracket. The nozzle bracket is rotatable about a fixed point on the protractor component. The protractor component provides incremental application angle setting information based on the setting of an application angle of the nozzle with respect to a top surface of the wafer.
In yet another aspect of the invention, an edge bead removal system is provided for removing an edge bead formed on a wafer by a photoresist material application system. The system comprises means for applying an edge bead solvent on the edge bead and means for adjusting an application angle of the means for applying an edge bead solvent on the edge bead.
Another aspect of the invention relates to a method for minimizing defects in an edge bead removal process. The method comprises the steps of providing an edge bead removal nozzle assembly having an adjustable application angle and setting the edge bead removal nozzle assembly to a first application angle. The edge bead removal developer is then applied to an edge bead formed on a photoresist spin coated onto a wafer and the defects formed on the photoresist due to the edge bead removal process is determined. Based on the defect level the application angle is adjusted and the steps of applying edge bead removal developer and the step of determining the defects formed until and acceptable defect level is achieved is repeated.
Yet another aspect of the present invention relates to an edge bead removal nozzle assembly for applying an edge bead removal solvent on an edge bead formed on a wafer by a photoresist material application system. The nozzle assembly comprises an edge bead removal nozzle disposed in a nozzle bracket and a protractor component coupled to the nozzle bracket. The nozzle bracket is rotatable about a fixed point on the protractor component. The nozzle assembly also includes a support bracket coupled to the protractor component wherein the protractor component is pivotable with respect to the support bracket. Additionally, the protractor component provides incremental application angle setting information based on the setting of an application angle of the nozzle with respect to a top surface of the wafer. The application angle is adjustable between 0xc2x0 and 20xc2x0.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.